The component in human body is the significant information for evaluating human health condition and is also the crucial standard for medical diagnose. The component is very low contents in the human body. The current testing method is to obtain the blood sample from finger tip, earlobe or vein, then use one-off reagent to handle chemical testing. This kind of invasive measurement is very complicate, painful and has the risk of infection. It restricts the on time and frequent measurement, and hampers the proper healthy treatment and management. In this respect, noninvasive human blood composition testing is of significant meaning in the treatment of disease and also in the research of disease.
Among every component of the human blood, glucose concentration is the most focused subject. Glucose concentration is the most effective index for diabetic diagnose and treatment. Diabetic is a kind of metabolic disturbance which is caused by the abnormal component of glucose, and also can result in some kind of severe complicating disease such as diabetic ketoacidosis, cardiovascular disease, renal failure, ablepsia, acrogenic gangrene and infection. Diabetic is now becoming one of the biggest threat to human health.
Kaiser [U.S. Pat. No. 4,169,676, Oct. 2, 1979] is the first one who uses optical method to test human component. Dähne [U.S. Pat. No. 4,655,225, Apr. 7, 1987] proposed to use dispersive near-infrared Spectrophotometers in the human component test. Today, the methods of human component measurement are mainly concerned of the following ways: polarization method, Raman spectrology, light scattering coefficient method, opto-acoustic spectral method, mid-infrared spectrology, near-infrared spectrology, optical Coherence Tomography (OCT), and so on. Polarization method's testing position is the eyeball which is difficult for the patient to accept; and the oculogyration may change the optical path and enlarge the testing mistake; and several components within the eyeball will disturb the polarization and the double refraction will interfere and reduce the transition light intensity; and the deflection angle of glucose solution too small to detect. The difficulty of Raman spectrum method is that the absorption and scattering signal in biological tissue are very weak and the background fluorescence interference comes from protein molecule is very powerful. Opto-acoustic spectrum method is too sensitive to the change of tissue structure and mid-infrared spectrum method is not very good at penetrating the tissue deeply enough.
The near infrared absorption, which wavelength range is 780 nm-2500 nm, is mainly caused by frequency doubling of the molecular vibration or combination frequency of several compounds which have the chemical bond X—H, such as C—H, and O—H, and N-H. Based on the characteristic absorption spectrum, the ingredient contents can be tested, and glucose can be done also. Recently, the progress of computer and chemometrics technology enhance the sensitivity, precision, accuracy and reliability of quantitative analysis dramatically, near infrared spectroscopy widely used in some crucial area such as pharmacy, agriculture and petroleum. Compared with middle infrared wavelength area, the detector has much higher sensitivity and response speed, the radiant efficiency of the light source is higher, its optical elements are more reliable, costless, and have less effect from the outside working environment. Little or no need for sample preparation so that it is suit for rapid field test and real-time analysis. Near infrared spectrum method has the merits of high-speed, nondestructive, high efficiency and also has high penetrating ability of human sap and parenchyma, therefore it is the proper test wavelength area for the measurement. A successful example is the success of noninvasive measuring of human blood oxygen saturation degree using near infrared light.
The key obstacles which reduce the accuracy of noninvasive near-infrared human components test lie in the following:                (1) The signal is always very weak because of the huge amount of water in tissue which absorbs light in near infrared region very effective. And the glucose concentration in the blood is low, which less than 0.1%, and its absorption in near infrared region is very weak. To detect the components in vivo requires the instrument with very high Signal-to-Noise ratio (SNR).        (2) Variety of measuring condition: The variety of testing condition such as testing position, and borne pressure, and the area of incident light, will greatly change the optical path of light transport in the tissue. And the signal caused by this change is much more significant than that caused by the variety of glucose concentration. It is difficult to immobilize this change condition or eliminate them, to obtain the useful signal.        (3) Variety of human physiological statue: The variety of human physiological statue changes the signal greatly, which is much bigger than that caused by concentration variety of the components. So, it results in the overwhelming of the useful signal for determining the concentration of the human component.        
The signal is the multi-result of blood component and optical character of the skin. Many components of human body have absorption in near infrared spectrum, at the mean time, these spectrum are often over overlapping. The light transportation process is very complicate and has lots of optical path between the emission and reception. As shown in FIG. 2, there is big randomness of optical length. In direct receiving light scheme, all of this optical path which has experienced lots of the absorption and scattering of the human tissue coming into the photoelectric detector and cause the high complexity of the signal.